1. Field of the Invention
The present invention relates to a carbon nanotube (CNT)-mesoporous carbon composite, a method of preparing the same, a supported catalyst, and a fuel cell, and more particularly, to a CNT-mesoporous carbon composite prepared using a CNT-mesoporous silica composite as a template, a method of preparing the CNT-mesoporous carbon composite, a supported catalyst using the CNT-mesoporous carbon composite as a support, and a fuel cell using the supported catalyst as an anode, cathode, or both anode and cathode.
2. Discussion of the Background
Fuel cells are clean energy sources that have received considerable interest as one of the alternatives for replacing fossil fuels.
A fuel cell is a power generating system that produces direct current electricity through an electrochemical reaction of fuel, such as hydrogen, natural gas, or methanol, with an oxidizing agent. In general, the fuel cell includes an anode (fuel electrode) where a supplied fuel is electrochemically oxidized, a cathode (air electrode) where the oxidizing agent is electrochemically reduced, and an electrolyte membrane which is interposed between the anode and the cathode to provide a path for transporting ions produced at the anode to the cathode. Electrons are generated through the oxidation of the fuel at the anode, work via an external circuit, and are then returned to the cathode to reduce the oxidizing agent. A fuel cell's catalyst is contained in the anode and the cathode and catalyzes the electrochemical reaction. Thus, many trials have been conducted to increase the activity of the catalyst used in the electrodes. The catalytic activity increases as the reaction surface area of the catalyst increases. Reaction surface area increases as the particle diameter of the catalyst decreases, and small particle diameter allows the catalyst particles to be uniformly distributed on the electrode. Where reaction surface area of the catalyst is increased, the surface area of the catalyst support should also be increased.
A catalyst support for the fuel cell should have a large surface area due to high porosity and a high electrical conductivity for the flow of electrons. Amorphous microporous carbon powders known as activated carbon or carbon black are widely used as catalyst support for the fuel cells.
Amorphous microporous carbon powders are generally prepared by chemically and/or physically activating a raw material, such as wood, peat, charcoal, coal, brown coal, coconut peel, and petroleum coke. After activation, the carbon has a pore size of about 1 nm or less and a specific surface area of about 60 m2/g to about 1000 m2/g. Specifically, Vulcan Black and Ketjen Black, which are commercial products widely used as catalyst support for fuel cells, have a specific surface area of about 230 m2/g and about 800 m2/g, respectively. Their primary particle diameter is about 100 nm or less.
However, the amorphous microporous carbon particles have poor interconnection of micropores. In particular, in a conventional direct methanol fuel cell (DMFC), a supported catalyst using the amorphous microporous carbon particles as a support has lower reactivity than a catalyst consisting only metal particles. However, using a catalyst consisting of only metal particles increases the cost of the DMFC significantly. Thus, the development of a carbon support capable of improving the reactivity of the catalyst without incurring the cost of a pure metal catalyst is required.
To overcome these problems, a mesoporous carbon molecular sieve is disclosed in Korean Patent Laid-Open Publication No. 2001-0001127. This patent discloses a method of preparing an ordered mesoporous carbon molecular sieve using a mesoporous silica, which is prepared using a surfactant as a template material. In the above method, based on nano-replication, the mesoporous silica, such as “MCM-48” and “SBA-1”, has micropores connected three-dimensionally by mesopores and is used as a template to prepare an ordered mesoporous carbon molecular sieve with micropores and mesopores, which have a uniform diameter and are regularly arranged. According to the definition of the International Union of Pure and Applied Chemistry (IUPAC), micropores refer to pores with a diameter of less than 2 nm and mesopores refer to pores with a diameter of 2 to 50 nm.
However, since the mesoporous carbon sieve is composed of amorphous carbon, it has a relatively low electrical conductivity. Therefore, there is a need to improve the electrical conductivity of the support and thus improve the performance of the fuel cell.